1. Field of the Invention
The invention relates to compatible polymer blends comprised of a polymer component containing cyclohexyl (meth)acrylate as a monomer, and further comprised of a polymer component containing styrene as a monomer.
2. Discussion of the Background
As a rule, different polymer species are considered to be incompatible; i.e., down to very small concentrations of one of the components, different polymer species do not form homogeneous phases, such as can be characterized by complete miscibility of the components.
Certain exceptions to this rule are of increasing interest and importance, particularly among scientists and engineers concerned with the theoretical significance of the phenomenon. Fully compatible blends of polymers show complete solubility (miscibility) in all mixing ratios.
A comprehensive presentation of miscible polymer systems is found in, e.g., Paul, D. R. et al., 1978, Polymer & Engineering Sci., 18, 16:1225-34; and J. Macromol. Sci. - Rev. Macromol. Chem. C., 18, 1:109-68 (1980).
To demonstrate miscibility, the glass temperature Tg or the so-called "optical method" (clarity of a film produced by film casting from a solution of the polymer blend) is often employed. See Brandrup and Immergut, "Polymer Handbook", 2nd Ed., III:211-213. An additional test for miscibility of different polymers is the existence of a lower critical solution temperature (LCST). (See German Patent Applications P 34 36 476.5 and P 34 36 477.3.) The existence of a LCST involves a phenomenon wherein as a clear, homogeneous polymer blend is heated it separates into phases and becomes optically turbid or opaque. According to the literature, this behavior is unambiguous proof that the original polymer blend was comprised of a single homogeneous phase at equilibrium Examples of miscibility are, e.g., the systems polyvinylidene fluoride/polymethyl methacrylate and polyvinylidene fluoride/polyethyl methacrylate (U.S. Pat. Nos. 3,253,060, 3,458,391, and 3,459,843). More recent results concerning "polymer blends" and their applicability have been reported by Robeson, L. M., 1984, Polym. Engineering & Sci., 24 8:587-97.
Styrene/maleic anhydride copolymers, and styrene/acrylonitrile copolymers, are compatible with polymethyl methacrylate ("PMMA") under certain conditions (Ger. OS 20 24 940). Improved service properties are claimed for molding compounds of this type. Also, polymethacrylates are compatible in certain blends with copolymers of styrene and monomers with hydroxy functions which promote formation of hydrogen bonds; e.g., copolymer of styrene and p-(2-hydroxyhexafluoroisopropyl)styrene (Min, B. Y., and Pearce, Eli M., 1981, Org. Coatings and Plast. Chem., 45:58-64); or e.g., copolymers of styrene and allyl alcohol (Cangelosi, F., and Shaw, M. T., 1983, Am. Chem. Soc. Div. Polym. Chem. Polymer Preprints, 24:258-9).
Polystyrene itself and other styrene-containing polymers are considered not compatible with PMMA. Thus, a miscibility of PMMA (m.w. 160,000) Of only 3.4 ppm in polystyrene, and only 7.5 ppm for PMMA of molecular weight 75,000 in polystyrene, is reported by Shaw, M. T., and Somani, R. H., 1984, Adv. Chem. Ser., No. 206, "Polym. Blends Compos. Multiphase Syst.", pp. 33-42 (Chem. Abstr. 101:73417e). Even relatively low molecular weight polystyrene is relatively incompatible with PMMA. Thus, a mixture of 20% of a very low molecular weight styrene oligomer (m.w. 3,100) in PMMA no longer gives a clear product. Polystyrene with an equally quite low molecular weight of 9,600 is merely translucent at 5% solution in PMMA (Parent, Raymond R., and Tompson, Edward V., 1978, J. Polym. Sci., Polym. Phys. Ed., 16, 1829-47).
Other polymethacrylates and polyacrylates similarly do not form transparent polymer blends with polystyrene These include polyethyl methacrylate, polybutyl methacrylate, polyisobutyl methacrylate, polyneopentyl methacrylate, polyhexyl methacrylate, and many others. See also Somani, R. H., and Shaw, M. T., 1981, Macromol., 14, 1549-54. Mechanical mixtures of polymers (polyblends) have led to plastic products with improved properties, in certain cases and in certain areas of the plastics industry (see Kirk-Othmer, 3rd Ed., J. Wiley, Vol. 18, 1982, pp. 443-78). The physical properties of such "polyblends" ordinarily represent a compromise, which can mean an overall improvement compared with the properties of the individual polymers. Under these circumstances, multiphase polymer mixtures have achieved greater commercial importance than compatible blends (see Kirk-Othmer, loc. cit., p. 449).
Multiphase and compatible polymer mixtures must therefore be kept strictly separate with regard to their physical properties as well as other properties relevant to application technology in particular their optical properties (transparence, clarity, etc.). As mentioned above, when it is sought to produce blends of plastics to yield an improved overall spectrum of properties, compatibility limitations often intervene. This appeared to be the situation for the two polymer classes of polystyrenes and polyalkyl (meth)acrylates. (See Kruse, W. A. et al., 1976, Makromol. Chem., 177, 1145; and Somani, R. H., and Shaw, M. T., loc. cit.)